A method of finding such buried people, which has become standard in particular for locating avalanche victims, is to search according to the transmitter-receiver principle. That is, a wireless transmitter carried by the buried person sends out signals that are received by a searcher, or a group of searchers, by means of a wireless receiver. To achieve a high degree of compatibility between an arbitrary number of transmitters and receivers, a standardized signal characteristic is employed. In the case of avalanche searches, for example, a frequency of 457 kHz is used.
The wireless receivers have available one or more antennae with a pronounced directional characteristic, and can be used to take a bearing on the site of origin of the signals, and thus to locate the position of the buried person.
The manufacturers of such wireless transmitters and/or receivers are continually developing these devices in order to make it easier to find one or more such buried persons. This is particularly important because the rescuers who operate the wireless receivers are under extreme stress: every second spent in locating the target can crucially determine whether the person or persons involved will live or die. One study, for example, has shown that the probability that a person caught in an avalanche will survive that experience decreases rapidly only 15 minutes after the event. Hence, modern wireless receivers employ display devices (cf. the document DE 35 31 726 C2) that additionally display the momentary strength of a signal received from a particular direction. This information can be represented, for example, in the form of data explicitly stating the distance between transmitter and receiver.
In practice, it has been found that the so-called last meters are often the most difficult stage in the search for a buried person. In this phase of “point localization”, the received information specifying a particular direction can often play only a very minor role, or can even be misleading because the searcher may well already be standing above the buried person. Distance data are also often erroneous in this stage, and exhibit only minimal differences.